Initializing a Vector in STL Using C++

Introduction

In this lab, we will learn about the different ways to initialize a vector in C++. We will cover the following methods:

Skills Graph

%%%%{init: {'theme':'neutral'}}%%%% flowchart RL cpp(("`C++`")) -.-> cpp/SyntaxandStyleGroup(["`Syntax and Style`"]) cpp(("`C++`")) -.-> cpp/BasicsGroup(["`Basics`"]) cpp(("`C++`")) -.-> cpp/ControlFlowGroup(["`Control Flow`"]) cpp/SyntaxandStyleGroup -.-> cpp/comments("`Comments`") cpp/BasicsGroup -.-> cpp/variables("`Variables`") cpp/BasicsGroup -.-> cpp/data_types("`Data Types`") cpp/BasicsGroup -.-> cpp/operators("`Operators`") cpp/ControlFlowGroup -.-> cpp/for_loop("`For Loop`") subgraph Lab Skills cpp/comments -.-> lab-96167{{"`Initializing a Vector in STL Using C++`"}} cpp/variables -.-> lab-96167{{"`Initializing a Vector in STL Using C++`"}} cpp/data_types -.-> lab-96167{{"`Initializing a Vector in STL Using C++`"}} cpp/operators -.-> lab-96167{{"`Initializing a Vector in STL Using C++`"}} cpp/for_loop -.-> lab-96167{{"`Initializing a Vector in STL Using C++`"}} end

Using push_back() method

The push_back() method is used to insert elements into the vector dynamically one at a time. This method increases the size of the vector by one and inserts the new element at the end of the vector.

#include<iostream>
#include<bits/stdc++.h>

using namespace std;

int main()
{
    cout << "Using push_back() method\n\n";

    //create an empty vector
    vector<int> v;

    //insert elements into the vector using push_back()
    v.push_back(1);
    v.push_back(2);
    v.push_back(3);

    //prining the vector
    cout << "The elements of the vector are: ";

    for (int i : v)
    {
        cout << i << " ";
    }

    cout << "\n\n\n";

    return 0;
}

To compile and run the above code, open the terminal and navigate to the file location ~/project. Type the following command to compile and run the program:

g++ main.cpp -o main && ./main

Initializing all the elements with a specific value

We can initialize all the elements in the vector with a specific value using the following constructor:

vector<int> v1(n, value);

Here, n represents the number of elements we want to initialize and value represents the value to which all the elements are to be initialized.

#include<iostream>
#include<bits/stdc++.h>

using namespace std;

int main()
{
    cout << "Initializing all the elements with a specific value\n\n";

    //creating a vector of size 5 with all values initalized to 10
    vector<int> v1(5, 10);

    //printing the vector
    cout << "The elements of the vector are: ";

    for (int i : v1)
    {
        cout << i << " ";
    }

    cout << "\n\n\n";

    return 0;
}